In general, an image, and particularly a multilevel image contain many pieces of information. In accumulating/transmitting such an image, the processing data amount is very large. To prevent this, an image is accumulated/transmitted using high-efficiency coding of reducing the data amount by removing the redundancy of the image while degradation of the image quality is permitted to a certain degree.
One of the high-efficiency coding methods is JPEG compression coding. According to this method, a multilevel image is transformed into a frequency component by DCT (Discrete Cosine Transformation) in units of blocks, and the obtained transformation coefficient is quantized to achieve variable-length coding.
In coding using DCT, a high compression ratio causes a block distortion in a decoded image. To solve this distortion, a new coding method using wavelet transformation has recently been proposed.
Variable-length coding is often applied as part of various high-efficiency coding methods.
However, a method of performing variable-length coding for a multilevel image with simple processing, and a processing apparatus for executing this variable-length coding method at a high speed have not been established yet.